Feasibility of FMC Pitch-Catch for Inspection of Pipeline Girth Welds
TWI Industrial Member Report 1166-2023 [pdf / 2987 KB]
By Miles Weston and Calum Hoyle
The combination of time-of-flight diffraction (ToFD) and pulse-echo techniques in automated ultrasonic testing (AUT) systems has become common place for inspection of pipeline girth welds in the oil and gas industry. AUT is often preferred to radiography, due to the reduced costs, detectability of planar flaw types and health and safety implications associated with ionising radiation.
This project presents the feasibility of replacing conventional ToFD channels with an ultrasonic array FMC pitch-catch setup to determine its reliability of detection, flaw sizing and locational accuracy for planar through wall flaws in pipeline girth weld components in comparison with current industry standard techniques.
By implementing a successful FMC pitch-catch setup there is potential for significant cost savings through reduced operator training, setup and increased reliability of inspection. It also offers the potential to perform FMC pulse-echo and FMC pitch-catch scans simultaneously, using a single pair of ultrasonic array transducers.
- Development of FMC pitch-catch calibration routines for system latency and probe separation distance form key steps to ensure reliable flaw detection and accurate through-all flaw sizing.
- Inspection of a girth weld pipe sample using the FMC pitch-catch technique, combined with pulse-echo and self-tandem inspection modes, achieved an average through wall sizing accuracy for lack of fusion flaws of 0.3mm. All flaws identified with FMC were present in the sectioning data.
- The FMC pitch-catch mode was shown to outperform the other available inspection modes in terms of through wall sizing accuracy by an average of 0.1mm, although all modes were required to ensure detection and sizing of all flaws.
- The FMC pitch-catch inspection mode is now included within BS ISO 23865:2021 and is considered ready for use by industry.
FMC girth weld setup, showing a cross sectional image of a 20mm thick plate weld containing a centreline EDM notch, imaged using FMC pitch-catch mode